Introduction: Dimensional changes in acrylic patterns during laboratory process to fabricate casting are an important issue which could lead to many clinical consequences. Microleakage, lack of retention and fitness are few of problems which could be predicted in the case of dimensional changes in acrylic patterns. So, investigating the factors which could minimize the dimensional change is necessary. This study compares how different proportions of silica-sol and distilled water affect the dimensional changes in castings. Methods: This study was an experimental study wherein 30 specimens of acrylic patterns (Duralay) with similar dimensions were prepared and equally divided in five different groups and studied. Using extensiometer digital machine, the acrylic patterns were measured at three portions (length, coronal diameter and apical diameter) with accuracy of 10 microns. Results: 1- The mean average of casting post length compared to changed acrylic patterns was statistically significant in pure distilled water group only. 2- The mean average of changes in casting coronal diameter did not demonstrate any significant differences compared to acrylic patterns. 3- The mean average of changes in casting post apical diameter compared to acrylic patterns using pure distilled water was significant. Conclusion: Because the least value in dimensional change was seen in ratio of silica-sol and distilled water, these ratios are recommended in fabrication of casting posts in order to have maximum accuracy and minimum micro leakage while building crowns and bridges.

Keywords: Casting posts, Dimensional change.

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